1. Technical Field
The present invention relates generally to image capture apparatus and more particularly to pixel array devices in such apparatus.
2. Background Art
Image capture apparatus, such as digital still and moving picture cameras, rely on image sensors. The image capture apparatus contains an array of image sensors, or light sensitive devices, detect the intensity of light received from the image. Each image sensor typically generates electronic signals that have amplitudes that are proportionate to the intensity of the light received by the image sensors. The image sensors can convert an optical image into a set of electronic signals. The electronic signals may also represent intensities of colors of light received by the image sensors. The electronic signals can be conditioned and sampled to allow image processing to provide an electronic version of the image.
Integration of the image sensors with signal processing circuitry is becoming more important because integration enables miniaturization and simplification of imaging systems. Integration of image sensors along with analog and digital signal processing circuitry allows electronic imaging systems to be low cost, compact and require low power consumption.
Historically, image sensors have predominantly been charged coupled devices (CCDs). CCDs are relatively small and can provide a high-fill factor. However, CCDs are very difficult to integrate with digital and analog circuitry. Further, CCDs dissipate large amounts of power and suffer from image smearing problems.
An alternative to CCD sensors is active pixel sensors. Active pixel sensors, such as photodiodes, can be fabricated using standard semiconductor CMOS processes. Therefore, active pixel sensors can easily be integrated with digital and analog signal processing circuitry. Further, CMOS circuits dissipate small amounts of power. One disadvantage to CMOS active pixel sensors is that the design must always be optimized among competing requirements of minimizing pixel area, maximizing photodiode collector sensitivity, and maximizing spacing of CMOS circuitry.
To overcome the above disadvantage, elevated active pixel sensors have been developed where the pixel sensors are elevated above the signal processing circuitry on the semiconductor wafer and connected by several levels of interconnect.
However, to avoid cross talk or interference between detected or generated signals within an array of elevated active pixel sensors, it is sometimes necessary to electrically isolate the pixel sensors from one another. Methods that have been proposed to isolate the pixel sensors include etching formed devices and depositing insulating films. Unfortunately, these methods resulted in the pixel sensors being exposed during processing and leakage paths forming through the intrinsic layer, or i-layer, between the pixel sensors, which resulted in increased noise. In addition, forming the insulating films increased process complexity, which added to manufacturing cost.
Solutions to these problems have been long sought, but have long eluded those skilled in the art.
The present invention provides an image sensor and method of manufacture therefor includes a substrate having pixel control circuitry. Dielectric layers on the substrate include interconnects in contact with the pixel control circuitry and with pixel electrodes. An intrinsic layer is over the pixel electrodes and has a gap provided between the pixel electrodes. An intrinsic-layer covering layer is over the intrinsic layer and a transparent contact layer over the intrinsic-layer covering and the interconnects. The intrinsic, intrinsic-layer covering, and transparent contact layer interact in different combinations to provide a pixel isolation system for the image sensor.
An advantage of the present invention is that the intrinsic layer is fully enclosed, and would minimize or eliminate leakage paths through the intrinsic layer that existed in the prior art.
An additional advantage is that the present invention does not require dielectric isolation. In fact, some embodiments would not require any additional masks.
Certain embodiments of the invention have other advantages in addition to or in place of those mentioned above. The advantages will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings.